fror - Developer IT

Quickly determine if a number is prime in Python for numbers < 1 billion

- by Frór

Hi, My current algorithm to check the primality of numbers in python is way to slow for numbers between 10 million and 1 billion. I want it to be improved knowing that I will never get numbers bigger than 1 billion. The context is that I can't get an implementation that is quick enough for solving problem 60 of project Euler: I'm getting the answer to the problem in 75 seconds where I need it in 60 seconds. http://projecteuler.net/index.php?section=problems&id=60 I have very few memory at my disposal so I can't store all the prime numbers below 1 billion. I'm currently using the standard trial division tuned with 6k±1. Is there anything better than this? Do I already need to get the Rabin-Miller method for numbers that are this large. primes_under_100 = [2, 3, 5, 7, 11, 13, 17, 19, 23, 29, 31, 37, 41, 43, 47, 53, 59, 61, 67, 71, 73, 79, 83, 89, 97] def isprime(n): if n <= 100: return n in primes_under_100 if n % 2 == 0 or n % 3 == 0: return False for f in range(5, int(n ** .5), 6): if n % f == 0 or n % (f + 2) == 0: return False return True How can I improve this algorithm?

Read the article

How do the versions of Guava work?

- by Frór

I would like to use Guava in a project, but my PM doesn't like the "r05" suffix, saying that it looks like it's not stable. In fact, the part I need is only the Google-Collections 1.0 which is now deprecated (my PM doesn't like that word either). So I don't really get the versioning of Guava/Google-Collections. I'm currently doing the development with GC1.0, but if possible I'll switch to a more recent and stable version.

Read the article

diff implementation in Java

- by Frór

Hi, I'm looking for a diff implementation in Java. I've seen that Python has its own SequenceMatcher (with difflib), which is exactly what I need... in Java. Is there any portage? Or is there any other class/library that performs the same in Java? If not, where can I find the source code of that difflib (if free as in speech) to make my own implementation of SequenceMatcher in Java ? Unfortunately, Apache Commons Lang doesn't help me much. Thanks!

Read the article

The Java interface doesn't declare any exception. How to manage checked exception of the implementat

- by Frór

Let's say I have the following Java interface that I may not modify: public interface MyInterface { public void doSomething(); } And now the class implementing it is like this: class MyImplementation implements MyInterface { public void doSomething() { try { // read file } catch (IOException e) { // what to do? } } } I can't recover from not reading the file. A subclass of RuntimeException can clearly help me, but I'm not sure if it's the right thing to do: the problem is that that exception would then not be documented in the class and a user of the class would possibly get that exception an know nothing about solving this. What can I do?

Read the article

Unable to add item to dataset in Linq to SQL

- by Mike B

I am having an issue adding an item to my dataset in Linq to SQL. I am using the exact same method in other tables with no problem. I suspect I know the problem but cannot find an answer (I also suspect all i really need is the right search term for Google). Please keep in mind this is a learning project (Although it is in use in a business) I have posted my code and datacontext below. What I am doing is: Create a view model (Relevant bits are shown) and a simple wpf window that allows editing of 3 properties that are bound to the category object. Category is from the datacontext. Edit works fine but add does not. If I check GetChangeSet() just before the db.submitChanges() call there are no adds, edits or deletes. I suspect an issue with the fact that a Category added without a Subcategory would be an orphan but I cannot seem to find the solution. Command code to open window: CategoryViewModel vm = new CategoryViewModel(); AddEditCategoryWindow window = new AddEditCategoryWindow(vm); window.ShowDialog(); ViewModel relevant stuff: public class CategoryViewModel : ViewModelBase { public Category category { get; set; } // Constructor used to Edit a Category public CategoryViewModel(Int16 categoryID) { db = new OITaskManagerDataContext(); category = QueryCategory(categoryID); } // Constructor used to Add a Category public CategoryViewModel() { db = new OITaskManagerDataContext(); category = new Category(); } } The code for saving changes: // Don't close window unless all controls are validated if (!vm.IsValid(this)) return; var changes = vm.db.GetChangeSet(); // DEBUG try { vm.db.SubmitChanges(ConflictMode.ContinueOnConflict); } catch (ChangeConflictException) { vm.db.ChangeConflicts.ResolveAll(RefreshMode.KeepChanges); vm.db.SubmitChanges(); } The Xaml (Edited fror brevity): <TextBox Text="{Binding category.CatName, Mode=TwoWay, ValidatesOnDataErrors=True, UpdateSourceTrigger=PropertyChanged}" /> <TextBox Text="{Binding category.CatDescription, ValidatesOnDataErrors=True, UpdateSourceTrigger=PropertyChanged}" /> <CheckBox IsChecked="{Binding category.CatIsInactive, Mode=TwoWay}" /> IssCategory in the Issues table is the old, text based category. This field is no longer used and will be removed from the database as soon as this is working and pushed live.

Developer IT